Banca de DEFESA: EDUARDO MOUSSALLE GRISSOLIA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : EDUARDO MOUSSALLE GRISSOLIA
DATE: 13/06/2022
TIME: 09:00
LOCAL: https://conferenciaweb.rnp.br
TITLE:

MINERALOGY, GEOCHEMISTRY AND SPATIAL VARIABILITY OF THE MORRO DO ENGENHO LATERITIC Ni DEPOSIT, ALKALINE PROVINCE OF GOIÁS

KEY WORDS:

Weathering. Laterite-hosted Ni and Co. Alkaline mafic-ultramafic rocks. Nibearing silicates. 3D

PAGES: 83
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SPECIALTY: Metalogenia
SUMMARY:

The Morro do Engenho Ni laterite deposit is the result of weathering processes on the alkaline maficultramafic rocks that compose the Cretaceous-age zoned intrusive body, belonging to the Alkaline Province of Goiás. Historically, the deposit is classified as a silicate type, where mineralization is present mainly, in phyllosilicates such as serpentine and chlorite. This study aims to understand the metallogenetic processes and controls acting on the mineralization of the lateritic Ni deposit of Morro do Engenho, through the identification of Ni-bearing mineral phases, lithogeochemical characterization of alteration profiles, and analysis of the spatial variability of concentrations. The methodology used included petrography, SEM/EDS, lithogeochemistry, three-dimensional modeling, and variography studies. The Morro do Engenho intrusive massif is formed by a dunitic core, surrounded by a peridotite/pyroxenitic zone, an alkaline gabbroic zone, and more externally by a syenite-nephelinic zone. The laterite profile is structured into eight alteration horizons, stacked from the bedrock as (i) saprock, (ii) lower saprolite, (iii) ferruginous saprolite, (iv) ochre saprolite, (v) plasma zone, (vi) duricrust laterite, (vii) silicified crust, and (viii) laterite soil. Ni mineralization is concentrated in the lower saprolite, the ferruginous saprolite, and the ochre saprolite. The results pointed to the presence of Ni in silicate mineral phases, represented by serpentine, chlorite, and smectite, as well as in oxidized phases, concentrated in Fe and Mn oxyhydroxides and spinels. The zones peripheral to the dunite core represent the most expressive Ni enrichment, where the contents can exceed 5.0%. Variogram analysis shows azimuth 175° as the direction of greatest continuity of mineralization. Using the 1.0% cut-off grade, the total resource was estimated at 31 Mt with an average grade of 1.26%, totaling 40 Mt of Ni contained metal. Silicate mineralization accounts for about 73% of the total resources, with the majority being in gabbroic. The evolution of the deposit was influenced by the South American (Paleogene) and Velhas (Neogene) geomorphological cycles. During the first cycle, there was the formation of silicified crusts that allowed, throughout the erosion that occurred in the second cycle, the preservation of the hilltops. This configuration kept previously enriched horizons elevated above the water table, which favored the leaching of Ni into the lower saprolite. Lateral groundwater movement transported Ni in solution to peripheral zones, producing mineralization in lateritic profiles derived from the peridotite/pyroxenitic and gabbroic zones. The main hydromorphic Ni dispersion flow occurred in the 175° direction and allowed for major enrichment at the southeastern edge. Subsequent vertical fluctuations of the water table gave rise to oxide mineralization in the profiles. The dominant mineralization at Morro do Engenho deposit is silicate type, concentrated in Mg hydro silicates and clay silicates. The discussions presented here contribute to understanding the metallogenetic processes acting in the genesis of lateritic Ni deposits from mafic-ultramafic bodies and provide subsidies for exploration campaigns for similar deposits.

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